Spiral bandsaws that cut better and have a longer service life are required in lumbering. In order to meet this demand, several methods have gained commercial acceptance; one method is to braze very hard tips (made of WC-Co sintered alloys) to the saw blade, and in another method, a Co-base hard-facing alloy, typically Stellite No. 1 composed of Co-30 wt % Cr-12 wt % W-2.5 wt % C, is manually padded on the saw blade with oxy-acetylene gas (hereunder referred to as gas padding) and the pad is subsequently hardened.
The ends of exhaust and intake valve stems in gasoline or diesel engines are forced into contact with the rocker arm every time the valves are opened or closed. Therefore, these valve stems are required to have a particularly great wear resistance and are usually gas padded with Stellite No. 1 followed by hardening the pad. Valve stems in small engines are not large enough in diameter to accommodate gas padding, but today, there exists an increasing demand for hardening a face hardening alloy pad that is supplied in small metered amounts.
In continuous casting of copper alloys, active metals are added in the form of a mother alloy. Since the molten metal stays for an extended period within the furnace, the active metal added is oxidized at the surface of the melt to cause variations in the alloy composition. In order to compensate for the loss of active metal due to oxidation, it is necessary to supply the molten metal with a small and metered additional amount of the active metal in a continuous fashion. However, in the present state of the art, such additional active metal is charged intermittently in metered amounts in the form of plates, blocks or shavings.
Welders that enable face-hardening alloys to be padded automatically on the blades of spiral bandsaws have recently been developed for the purpose of automating padding, cutting and finishing operations. Efforts are being made to develop a welder that is capable of automatic padding of intake and exhaust valve stems. Another topic that is under serious consideration is how to automate the addition of active metals in the continuous casting of copper alloys.
Granules and spherical particles that easily roll about themselves are considered to be the best form of the padding alloy or mother alloy fed in automated processes, and the method of feeding rolling granules or spheroidal particles continuously and in metered amounts is gaining increasing acceptance in the industry. Therefore, the current automatic welder for padding a face-hardening alloy is fed with the alloy in granules rather than rods. Furthermore, there is an increasing demand for replenishing a molten copper alloy with spheroidal particles of an active metal having a constant weight.
Therefore, the preparation of spheroidal metal particles having uniformity in size is absolutely necessary for automating the feeding of padding alloys or mother alloys. Various techniques have been proposed and are currently used for making metal particles directly from a melt. However, making spheroidal metal or alloy particles from a melt (hereunder the term "metal particles" will include alloy particles) is very difficult and involves the following problems yet to be solved.
The techniques for making granules directly from a melt are primarily used with low-melting metals such as tin, lead and zinc. In one typical method, a molten metal is poured over a perforated tundish (receptacle having many small holes) and the dripping melt is dropped into water or an oil of low viscosity so as to solidify the melt. However, this method produces either teardrops or unevenly sized globules. In addition, the globules are either deformed or finely dispersed when they drop into water or oil. For these reasons, the method shown above fails to provide a high yield of spherical metal particles having a predetermined size.
A further problem with this method is that it cannot be applied to metals or alloys such as Stellite No. 1 which have high melting points and are very low in ductility since quenched globules will crack due to thermal strain.